Question

почему "имя" не подлежит замене здесь.

var foo = '<div>    <label class="required">_1_label__</label><div id="project_frontendbundle_car_1___name__"><div>    <label for="project_frontendbundle_car_carImages___name___position" class="required">Position</label><input type="number" id="project_frontendbundle_car_carImages___name___position" name="project_frontendbundle_car[carImages][__name__][position]" required="required" /></div><div>    <label for="project_frontendbundle_car_carImages___name___fileName">File name</label><input type="text" id="project_frontendbundle_car_carImages___name___fileName" name="project_frontendbundle_car[carImages][__name__][fileName]" maxlength="2000" /></div></div></div>'; 
 

 
var bar = foo.replace('_name_', '1'); 
 
$('body').text(bar);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

Answer 1

Попробуйте

var bar = foo.replace(/_name_/g, '1'); 

г = Глобально заменить